Acids and Bases in Slurries
The use of acids and bases for controlling pH in slurries is widely known. Buffering agents are employed to provide a buffered environment in which moderate amounts of either a strong base or acid may be added without causing any large change in pH. A buffer solution usually contains a weak acid and a salt of the weak acid, an acid salt with a normal salt or a mixture of two acid salts.
Coulter et al., in U.S. Pat. No. 3,743,613, disclose a particulate galactomannan gum based composition for sealing permeable formations. The composition contains a pH control agent to maintain pH of the initial slurry at about 7.5, preferably in the range of 8-12. A hydroxyl ion source such as any soluble or partially soluble hydroxide or carbonate in an amount to yield the desired pH may be used. Suitable buffering agents which may be employed to provide to provide the desired pH are NaH.sub.2 PO.sub.4 /Na.sub.2 HPO.sub.4, boric acid/sodium hydroxide, acetic acid/sodium hydroxide, boric acid/borax, sodium carbonate/sodium bicarbonate, and sodium bicarbonate.
Scher and Cochran, in U.S. Pat. No. 4,155,741, disclose a stable suspension-buffer system for aqueous suspension of microencapsulated materials which can be obtained by using aluminum hydroxide or ferric hydroxide as the suspending and buffering agent. Also used are a sequestering agent and a second suspending agent to prevent separation and caking.
Higgins, in U.S. Pat. No. 4,161,566, disclose aqueous disperse compositions that may include buffers such as potassium dichromate/acetic acid and potassium dichromate/phosphoric acid combinations.
In JP-58-002215 published Jan. 7, 1983, aqueous zeolite slurried are disclosed comprising carboxymethyl cellulose (CMC) as a dispersant and a water soluble alkali metal salt. The slurry is disclosed as being suitable for use as a detergent builder due to its excellent metal ion masking effect, buffer activity under alkaline conditions and a redeposition preventing effect.
Nayar et al., in U.S. Pat. No. 4,623,476, disclose stable suspensions of pigmets in aqueous hypochlorite bleach compositions. Bleach stable inorganic buffering agents from about 0.2 to 10% by weight are disclosed that maintain composition pH within the range of 10.5-13.5. Sodium carbonate, calcium bicarbonate, sodium sesquicarbonate, sodium silicates, sodium orthophosphate, and sodium tetraborate are disclosed as buffering agents.
Duminy-Kovarik, in U.S. Pat. No. 4,701,275, discloses an aqueous testing system for testing slurries of magnetic particles, wherein the slurry comprises a buffering element to assist in corrosion resistance. Boric acid buffering is preferred.
Gottwald and Machoczek, in U.S. Pat. No. 4,861,592, disclose a pharmaceutical composition suitable for oral administration comprising particulate cimetidine suspended in an aqueous phase containing a buffer which maintains the pH at greater than 7 and a suspending agent. Antacids such as aluminum hydroxide, magnesium hydroxide, magnesium carbonate, calcium carbonate, and mixtures are disclosed as agents that may be incorporated in the composition in order to maintain the pH greater than 8.
Motola et al., in U.S. Pat. No. 4,975,465, disclose a liquid aqueous based ibuprofen composition, wherein the ibuprofen is maintained in suspension by a combination of primary suspending agents and wherein a buffer acid is incorporated to adjust the pH of the composition to between 1.5 and 3.5. Compositions containing citric acid or phosphoric acid in an amount of 0.1% to 2% weight by volume are suggested. Sodium benzoate/citric acid and sodium benzoate/phosphoric acid containing ibuprofen compositions are disclosed.
Usagawa et al., in EP 0 435 561 A3, disclose silver halide materials containing solid particle dispersions of acidic 2-pyrazoline-5-one based filter dyes. Usagawa et al. teach the addition of small amounts of organic acids, such as acetic acid, citric acid, oxalic acid, and tartaric acid for the adjustment of pH.
Stude et al., in DE 4 103 283 A, disclose an interlayer material for separating stored glass sheets.